1. Field of the Invention
The present invention relates to the field of safe and arming of dangerous explosive devices. In particular, the present invention relates to safe and arming of weapons and ordnance devices.
There are a variety of applications for safe and arming devices that are dangerous by their very nature. This is particularly true where explosives are employed. Thus, in a non-military application where an explosive charge is being used in, for example, an oil field operation there are situations where it is desirable to have a safe and arm device associated with the explosives in order to protect the users and provide a degree of safety which is necessary during the course of placing the explosive for the particular application. Likewise, there are obviously numerous military applications involving explosive ordnance which require and demand the use of a safe and arming device. This is particularly true in situations where ordnance is aircraft delivered. In such situations, it is highly desirable that the ordnance be released from the aircraft and that arming not take place until after that ordnance has cleared the flight path and is not any longer in close proximity to the aircraft. The safe and arm device should, of course, keep the ordnance in a safe condition from the time it is assembled as a complete system at the manufacturing site until after it is launched from the aircraft or other launch vehicle. That is, it is obviously important that the ordnance or weapon system not be able to accidentally or otherwise be put into an operational condition during the shipping, handling, storage and other prelaunch environment situations.
One approach to safe and arming an ordnance device is to have the elements or components in the explosive train positioned so that the train is interrupted prior to the time the device is to be armed. In such a system when the ordnance device is being prepared for use, all of the elements of the explosive train are misaligned and maintained out of position until a manual or automatic sequence of events typically triggered by a post-launch event occur. This triggering like the sequence of events may be manual or automatic. With a misaligned explosive train the intent is obviously to see to it that a number of events are required to take place before alignment occurs and full access to the primary warhead explosive can result. Alignment may be accomplished electrically, mechanically, or electro-mechanically and arming may additionally require electronically controlled events to occur and signals to be present at specific times in the re-alignment sequence. It is only when all of the components or elements of the safe arm system and the components in the explosive train preceding the warhead explosive are placed in the proper alignment and all appropriate signals are received in combination and in the proper sequence that the warhead can be detonated.
In an earlier type of safe and arm system, barriers were introduced into the electrical, mechanical, electromechanical or electronic chain of events preceding the actual arming act such that unless all barriers were removed in the proper sequence the primary explosive, that is, the warhead could not be detonated. The complication of a multitude of barriers with one or more types or combination of types of schemes for moving such barriers resulted in many situations where the ordnance device became a dud and was unable to be fired. A single failure in the chain resulted in a totally inoperative ordnance device. Also, the more complicated the chain, the less likely pre-use troubleshooting and recovery would be successful. Thus, it is important that whatever scheme is used for safe and arming purposes, whether requiring realignment of misaligned components or removal of prepositioned barriers, the chain or sequence of events, used to bring components into alignment or to remove barriers must be such that the arming chain of events that will permit the primary explosive to be detonated can safely and reliably occur at the exact time required and not before. In considering the types of safe and arm devices it is important also to consider device reliability. It is particularly important in situations involving aircraft-launched ordnance that crew safety be assured. The safe and arm device must, therefore, be simple and reliable so that the crew is not put in an unsafe situation where a weapon can be unintentionally armed prior to release from the launch aircraft. Also it is important that the weapon upon launch and delivery not be a dud. Obviously the weapon should be in a safe condition during all prelaunch and preflight handling and storing operations.
2. Description of the Prior Art
Two types of prior art systems that take advantage of alignment and sequencing are the in-line systems and out-of-line systems. In the in-line systems electrical power comes from a missile thermal battery, for example, and a series of sensors then verify that the missile is following the desired post launch sequence. In an out-of-line system hot gases from weapon propellant exhaust pushes against a piston which then arms the fuze mechanically. Electrical power to complete the arming function comes from the missile thermal battery.
Mechanical safe and arm devices of the prior art have typically suffered from the types of problems one would expect from most mechanical systems. That is, there are typically a number of failure modes that are directly related to the number and types of interrupting elements or components within the mechanical system that must be actuated to make the mechanical device work properly. Thus it has been found not to be true that the more mechanical interruptions or barriers that are placed in the safe arm chain to the primary explosive the safer the device. If the intent is to make the device safe by having a more complex mechanical safe and arm implementation, one may find that although the safe and arm device fails in the safe mode, the weapon system or ordnance that was delivered in effect has become a dud. This may result in the delivering aircraft and flight crew being subjected to operating and environment hazards because of the weapon failure.
Many of the current safe and arm devices are tending to use purely electronic devices for the safe and arming function and any time delays that are required in relation to such functions. Time delays in the safe and arm systems that are primarily mechanical or electro-mechanical are typically more difficult to control than are those obtained by means which are purely electronic in nature. Electronic safe and arm devices including electronic time delay capabilities are, however, not without their faults. Power failures and device failures may result in a total loss of output of the device or of its time delay feature. Another failure mode involves a runaway condition in the electronic device or circuit. Some types of electrical devices or electronic devices are subject to outside interference. Thus in the use of such devices one must be concerned that the ordnance or weapon to which such a safe and arm device is attached may be triggered prematurely during preflight or prelaunch operations. What is in fact needed is a very simple device whether it be electrical, electro-mechanical, or electronic that provides a greater assurance of its operative condition and which does not have a failure mode which is totally detrimental to the mission in which the ordnance item is required.